BleepingComputer.com: stop using Firefox beta first run start page

I have several versions of firefox. Trouble is, if they are a beta or nightly build, every time I use a different version, then switch back, I get the "first time run" page like "thank you for using a beta" or whatever. I can't find a setting to kill this off. Start with blank page has no effect. Is there maybe an about:config that will stop it from doing this?